Performance Question: Rear Mounted Turbo Set-Up

[90TGP]

Ok, everyone knows that the major things holding us back on putting in a larger turbo, is A) the T25 flange engine space C) Injectors D) Tuning. Well I don't have a solution for C&D, but I have an idea for A&B.

 

I've been seeing more and more rear mounted turb set-ups appearing on F-Body's and Corvettes. http://www.jlturbo.com/info.htm

 

With the turbo out of the engine bay, you would drastically reduce engine heat, and free up a lot of room. You could also do a 3x00 topend swap and exhaust manifold swap without having to worry about modifying the exhaust manifolds to work with the cross-x pipe.

 

With the turbo under the car, you don't have to worry about heat soak since the filter would be getting cold air.

 

 

And talk about a sleeper set-up. If anyone asks you to pop the hood, you can show them your "cold air" intake.

 

 

Any comments?

[Jcrow]

they claim that they use a specially sized turbo. How would you go about sizing it? I assume the compressor would stay the same, but the exhaust housing would probably be bigger or smaller. All the current sizing methods are for using the turbo where the exhaust is hottest. I was looking under my car and there isn't much room under there. Another problem would be where to put the air intake. I wouldn't want mine behind the tires like that.

I plan to move my battery to the trunk and put the turbo up front where the battery used to be.

[Intlcutlass]

I wouldn't trust that. Puddle or any other obstruction comes along and your screwd. When that thing gets hot, and if driven where their might be water the constant water to dry water to dry would shorted the life IMO. Turbos belong where the engine is IMO.

[90TGP]

I was reading a post on ls1tech.com, a guy made 750+ rwhp with the rear mounted turbo on his Vette. I think he used a T76 turbo.

[Jcrow]

I got this on their website:

Don't turbos have to be really hot to work properly?

Putting a torch to your turbo and getting it hot doesn't produce boost. What produces boost is airflow across the turbine which causes the turbine to spin. If turbochargers required very high temperatures to produce boost, Diesel trucks and Methanol Race cars wouldn't be able to run turbos. However, each of these "Low Exhaust Temperature" vehicles work very well with turbochargers when, like any turbo application, the turbocharger is sized correctly.

In a conventional, exhaust manifold mounted turbocharger system, the extra heat causes the air molecules to separate and the gas becomes "thinner" because of the extra space between the molecules. This extra space increases the volume of air but doesn't increase the mass of the air. Because the volume is higher, the velocity of the gas has to be higher to get it out in the same amount of time.

 

By mounting the turbo further downstream, the gasses do lose heat energy and velocity, however, there is just as much mass (the amount of air) coming out of the tailpipe as there is coming out of the heads. So you are driving the turbine with a "denser" gas charge. The same number of molecules per second are striking the turbine and flowing across the turbine at 1200F as there is at 1700F.

 

Front mounted turbos typically run an A/R ratio turbine housing about 2 sizes larger because the velocity is already in the gasses and the volume is so big that the turbine housing must be larger to not cause a major restriction in the exhaust system which would cause more backpressure. With the remote mounted turbo, the gasses have condensed and the volume is less, so a smaller A/R ratio turbine housing can be used which increases the velocity of the gasses while not causing any extra backpressure because the gas volume is smaller and denser.

 

Sizing is everything with turbos. There is more to sizing a turbo for an application than cubic inches, Volumetric Efficiency, and RPM ranges. A turbo must also be sized for the exhaust temperatures. A turbine housing sized for 1700F gasses would have lag if the gasses were 1200F. This is why turbo cars have lag when they are cold and not warmed up yet. Both systems work well if sized correctly.

 

 

You might be able to get away with a 4 cylinder turbine housing

[jeremy]

I really want to try that on my cutty

[Jcrow]

check out the videos on their website

[GnatGoSplat]

I've seen a lot of Silverado SS guys using the STS Turbo. http://www.ststurbo.com/ I'm not sure why since there's plenty of underhood space in a Silverado.

 

I don't know if it's a good idea, I don't know if I'd want my car sucking intake air from underneath. Also, how about oil and coolant lines to the turbo? That's a whole lot of plumbing that has to go a pretty good distance.

[Jcrow]

another drawback is, you need an electric oil pump to get the oil back to the engine. They say in the website there is an alarm if that pump fails, but what do you do? pull over and wait? extra parts to break

[loominaz34]

They use a scavenging pump system that fits between the filter and the oil pan. the oil that goes through the turbo then is just drained back into the filler neck. the alarm sounds when there is not sufficient pressure in the oil lines IE: a line breaking. The only oil pump used is already in your car. I personally think this systemis a great idea because the intake tubing works as an intercooler, an intercooler with about 50% efficiency and less pressure drop than an intercooler of the same cooling capacity. I'll try to scan the article on the sts turbo system I have in my issue of "turbo and high tech performance"

[GutlessSupreme]

I thought you're supposed to limit piping length and bends, not promote them now we have the intake AND exhaust (for turbo) coming from 10+ feet away from the engine? sorry, but that's gone against every thing I've ever learned. Not to mention having the intake mounted nearly on the ground, underneath the car is just asking for something bad to happen, and the filter would have to be changed like once a month, if not more often..

[mfewtrail]

If you did that on a relatively small engine, I would imagine you're only going to start getting power in the upper rpms w/ a decent sized turbo wayyy back there. With a V8 like most(all?) of the kits are for, that's not much of a problem because they arlready make a great deal of torque.

[timg]

 

Neat idea, but I definitely disagree with their "reasoning" about efficiency. The arguments about emissions are good, but this is just as likely to be illegal as a conventional setup IMO. I think it would be interesting to put some equations into Excel and see if their theories hold up. Based on my gas turbines and thermo/fluids classes, I doubt it.

 

Tim

[buckethead]

My only concern is that you're putting that setup in a lot of danger from either speed bumps or moisture and dirt. I'd think that having the intake right under your car would be a bad idea, especially when there is snow on the ground. As far as the system working well, excluding the increased damage risk, all that i've read on those systems seem to say they work quite well. I read an article in my truckin magazine on the rear turbo setup some guy had in his custom truck. They said that it seemed to work just as well as any conventional turbo setup. I wonder, if it might even have an advantage in that you could use headers to improve flow to the turbo. I also seem to remember them suggesting building a seperate oil resevoir and pump setup exclusively for the turbo, that might help prevent line problems. If i were to try it, i'd try to build some sort of skidplate to protect the turbo, and I'd probably try to relocate the intake to a less moisture and dirt prone spot (perhaps up inside the rear fenderwell?)